Wetter Than Normal November Eases Drought to Slight

31 12 2018

Dale C. S. Destin |

DroughtMeterNovember’s rainfall was higher than usual – 135% of the average for the month. The total of 204 mm (8.03 in) makes this November the 21 wettest on record. The very welcome rainfall has ease the meteorological drought to slight levels and have also eased or eliminated other droughts.

Over 95% of the rainfall for November fell during the first 15 days of the month, making it the second wettest such period on record. The rainfall was caused by a cold front and a series of troughs.

The last three-month period – September to November, upon which the assessment of the current intensity of the drought is based, was slight dry. Notwithstanding a wetter than normal November, the last three months, as a time interval, had below normal rainfall with 370.6 mm (14.59 in) recorded. This is the lowest since 2015 and the second lowest since 2009.

RainfallAccuForPast24Months

Rainfall for the past 24 months for varying time intervals compared to the normal/average and records

We remain in a severe meteorological drought, the worst category on our drought scale. However, at the moment, the current intensity is slight. Recall that the overall description of the drought is based on the worst intensity achieve during its lifetime; however, over time, the intensity will fluctuate. Last month the intensity was at serious levels.

Potworks Dam, with a billion-gallon capacity, has moved from near totally dry to being one-third full, two-third empty – depending on your perspective. The water levels have gone above extraction height and I am advised that the same is true for the other smaller catchments.

Potworks Dams Nov13_2018_KarenCarbin

Potworks Dam – Nov 13, 2018. Complements Karen Corbin of the Humane Society

Potable water has become more readily available and water rationing has apparently cease, for now. This is indicative of huge dent November’s rainfall made on the droughts.

The fourteen-month period – October 2017 to November 2018, the duration of the drought thus far, is deemed severely dry. The total for the last 14 months of 977.6 mm (38.49 in) is the second lowest since 2001 – only the similar period October 2014 to November 2015 was drier. October of one year to November of the next normally gets 1514.6 mm (59.63 in), which means that there is a large rainfall deficit of around 35% – more than one-third of the usual rain did not fall.

Based on the last set of rainfall forecasts from regional and especially international sources, the news is discouraging with respect to rainfall. Overall, below normal rainfall is most likely for the next six months – January to June 2019, with relatively high confidence that the period January to March 2019 will be drier than normal – possibly well below normal. Thus, there is every reason to believe that the droughts will continue and likely reintensify. The chance of the droughts ending is, at most 30% or low.

MultimodelEnsembleRainfall_JFM_2019

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Jan-Mar 2019, based on 12 global model

On average, our severe meteorological droughts last for around 16 months, but not continuously at severe intensity. At current, the drought is in its 15th month; the longest such drought on record lasted 38 months – Jul 2013 to August 2016.

I now expected 2018 to be among the top 10 direst years on record with the island-average total less than 900 mm or less than 35 inches. We normally get 1206.5 mm or 47.5 inches.

AccumulationJan_Dec2018

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All the best for 2019!





Steep Pressure Gradient to Cause Hazardous Conditions Across the Region

27 12 2018

Dale C. S. Destin|

Strong and gusty winds are forecast to move across most of the Caribbean this weekend – Friday through Sunday. These winds will make for hazardous conditions onshore and especially offshore. Some activities on land will become dangerous and marine conditions will be very hazardous for small craft operators.

The high winds and seas may be reminiscent of the passage of a weak tropical storm, but they won’t be due to any such system. The elevated winds will be the result of a very steep pressure gradient, due to the strength and location of the centre of a high-pressure system. The pressure gradient – the horizontal change of pressure, will be around 25% higher than normal.

Very hazardous seas in excess of 2.5 metres and rising to 3.5 metres (9 to 12 feet) will take place Friday through Sunday across the northeast Caribbean. Winds and seas will start building on Thursday – peaking on Saturday. Seas will occasionally reach 4.5 metres (15 feet).

These hazardous conditions will peak about a day earlier across the western Caribbean (including the Bahamas) and a day later across the southern Caribbean.

The winds will range between 34 and 45 km/h (21 and 32 mph) across the northeast Caribbean Friday through Sunday. Gusts to gale-force i.e. 64 km/h (40 mph) are expected. These kinds of winds very unusual for the region outside of being associated with a tropical cyclone (hurricane, tropical storm or tropical depression). The wind will generally blow from the east.

Possible impacts of the strong winds and hazardous seas include:

  • injuries or loss of life;
  • damage or loss of boats and fishing equipment;
  • disruptions to marine recreation and businesses;
  • disruptions to air and especially sea transportation;
  • disruptions to outdoor sporting activities;
  • disruptions of sea search and rescue;
  • scarcity of sea food;
  • vehicular accidents and
  • economic losses.

The worst affected area is likely to be the northern Caribbean – including the Leeward Islands and areas further west. Marine warnings are expected to be issued by most islands. Winds will be strongest over open waters, elevated terrains and windward coastal areas – eastern coastal areas.

Small craft operators and even some not so small crafts operators should stay in or very near port this weekend. Work at high and exposed evaluations should be avoided. Some outdoor activities may need to be postponed or adjusted for the conditions. Secure or take indoors light and loose objects – patio furniture, trash can etc..

Be very caution if you need to drive a high-profile vehicle, as strong winds could make for difficult, if not dangerous, driving of such automobile.

This event is not related to a tropical cyclone; nonetheless, some measures need to be put in place to mitigate the potential impacts – especially those related to the marine environment.

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The 2018 Atlantic Hurricane Season Summary

2 12 2018

Dale C. S. Destin |

The 2018 Atlantic Hurricane Season came to an uneventful end yesterday. However, it was the third consecutive above normal/active season – leaving deaths and destruction in its wake.HurTracks2018

It will be remembered by the region (Caribbean), not for its activity, but because the islands were generally spared its activity following on the heels of the catastrophic/cataclysmic 2017 season. Many islands in the Caribbean are still very far from full recovery from last year, and another similar such season would have caused things to go from extremely bad to double horrendously bad (so to speak).

The season produced 15 named storms (NSs), 8 of which become hurricanes (Hs) and 2 intensified into major hurricanes (MHs) – Category 3 and over. The Accumulated Cyclone Energy (ACE), a measure of the overall activity of the season, was 128. The ACE last years was 225.

A normal season produces 12 NSs, 6 Hs, 3 MHs and 106 ACE. Relative to a normal season, this season had 25% more NSs than normal, 33% more Hs, 33% less MHs and 21% more ACE than normal.

The active 2018 Atlantic Hurricane Season left in its wake 154 deaths and around 34 billion dollars in damage. The strongest hurricane was Michael with 250 km/h (155 mph) winds. It was also the deadliest with 60 deaths. The most destructive was Florence with over $17.9 billion.

Relative to Antigua and Barbuda

It was an inactive season for our islands. No tropical cyclone (depression, tropical storm, hurricane) affected Antigua and Barbuda i.e. came within 193 km (120 mi). Isaac came the closest but still passed over 222 km (138 mi) to our south – between Dominica and Martinique.

Relative to the Rest of the Caribbean

The Caribbean saw four tropical cyclones entering or forming in the area – Tropical Storms Alberto, Isaac and Kirk, and MH Michael. Alberto proved the deadliest for the region, killing 10 persons in Cuba. Michael was also very impactful to western Cuba; however, no deaths were reported.

Seasonal forecast

I issued five forecasts for the 2018 season – these were for mainly above normal activity:

2018HurricaneSeasonGraphic

Interestingly, my best forecast was issued in April and the second best was issued in May. It is interesting because usually the earlier forecasts are the least skilful, while the latest (August forecasts) are the most skilful. However, in this case, the first was best and the last (August) tied with June for the worst. Notwithstanding, all forecasts captured the numbers for the season within the ranges issued – the 70% confidence interval.

Of the over 25 groups who have submitted their seasonal forecast to the website – http://seasonalhurricanepredictions.bsc.es/, most forecast a near normal season w.r.t. hurricanes – six. Further, as the season went by, most groups downgraded their forecasts – calling for a near to below average season. It is also noted that the average number of hurricanes predicted went from eight in March/April to 5 by July/August. Meanwhile, the number of named storms went from 13 in March/April to 11 by July/August.

Like me, most groups decreased the amount of activity initially forecast for the season. However, (with humility) my forecast was among the better forecasts – doing similar to or better than notable groups such as National Oceanic and Atmospheric Administration (NOAA), Colorado State University (CSU), United Kingdom Met Office (UKMET), and Tropical Storm Risk (TSR).

Notable records

The 2018 season is the first and only on record to see seven storms that were subtropical in nature at some point in their lifetimes. These are (Alberto, Beryl, Debby, Ernesto, Joyce, Leslie, and Oscar).

On October 11, for the first time in history, a tropical storm warning was issued for Madeira. This was due to Leslie, which became the first tropical cyclone to pass within 160 km (100 mi) of the archipelago since reliable record-keeping began in 1851.

Good riddance to you hurricane season. We wish never to see you again but we know only too well that you will be back in seven months – June 1 to November 30. Nevertheless, we will be prepared!








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